U.S. application Ser. No. 464,099, filed Apr. 25, 1974, now U.S. Pat. No. 4,225,481, and the disclosure of which is herein incorporated by reference, relates to a process for the production of dispersions of aminoplast condensates in organic polyhydroxyl compounds, in which the production of the aminoplast condensates by the oligocondensation or polycondensation of substances capable of forming aminoplasts known per se, is carried out in the organic polyhydroxyl compounds as reaction medium.
The dispersions according to Ser. No. 464,099, now U.S. Pat. No. 4,225,481, show a number of remarkable advantages which are discussed in detail in the application.
Unfortunately, one disadvantage of most of the dispersions described in the application is the fact that they still contain small quantities of free formaldehyde and free, unreacted N-methylol groups. In addition to the strong odors given off, especially when these dispersions are used as reactants for polyisocyanates in the production of polyurethane foams, this results in the unfavorable side effect that the foams are not shrinkage-resistant. In other words, the foams produced therefrom do not retain their volume on completion of foaming, but instead show signs of shrinkage.
Although it was proposed in Example 6 of Ser. No. 464,099 to eliminate free formaldehyde in the aminoplast dispersions by treatment with gaseous ammonia to form hexamethylene tetramine, the total insolubility of the hexamethylene tetramine in the polyether used (and presumably its pronounced crystallinity in the cell "bridges" of the foams) surprisingly produced a marked decrease in the tensile strength of the foams produced therefrom.